This changes the thread header positioning of the
unread indicator to match the designs based on the route:
1. When the channel is open, show the indicator of # unread
threads with the icon
2. When the threads list is open, show no indicator since
you are on the list and can see which threads are unread
3. When a single thread is open, show the unread threads
indicator along with a left < back button, with a label
to show that this goes back to ongoing discussions
Drawer changes to come in another PR.
6ec6cfccf8